An exemplary base line injector is depicted at 10 in prior art FIG. 1. Reference may be had to U.S. Pat. No. 5,460,329, incorporated herein by reference, for additional detail on injector 10. The injector 10 has a housing 12 that is disposable in a receiver defined in an engine head. An injector module 14 is disposed within an aperture defined in the housing 12.
The principal operating components of the prior art injector 10 include the control valve assembly 16, intensifier assembly 18, and needle valve assembly 20.
The control valve assembly 16 includes a translatable spool 22 that is transversely translatable under the influence of at least one solenoid 24. It is understood that while two solenoids 24 are depicted, one of the solenoids 24 could be replaced by a return spring or other biasing element.
The spool 22 is selectively in fluid communication with an actuating fluid inlet 0.26 and an actuating fluid vent 28. The spool 22 is further in fluid communication with an actuating fluid passageway 30. The actuating fluid that is preferably utilized with the injector 10 is engine lubricating oil at elevated pressures of generally 450–3,000 psi. It is understood that other suitable actuating fluids could be used as well, including without limitation, engine fuel.
The intensifier assembly 18 includes a translatable piston 32 and a depending plunger 34. In practice, the piston 32 and plunger 34 are formed integral as a single component.
The piston 32 has a piston head 36 that has a selected area. The piston head 36 resides in and defines in part an actuation chamber 38. The actuation chamber 38 is in fluid communication with the actuation fluid passageway 30. Fluid pressure in the actuation chamber 38 generates a downward directed force on the piston head 36. An intensifier return spring 40 bears on the underside of the piston 36 and exerts a bias on the piston 32 in opposition to any force generated by fluid pressure acting on the piston head 36.
The plunger 34 includes a plunger head 42 having a selected area. The plunger head 42 is translatably disposed in a plunger chamber 44. A checked fuel refill 46 is selectively in fluid communication with a fuel gallery and with the plunger chamber 44 for providing a volume of fuel to the injector 10 to be injected into the combustion chamber.
A high pressure fuel passage 48 is in fluid communication with the plunger chamber 44. The high pressure fuel passage 48 effects a fluid communication between the plunger chamber 44 and the needle valve assembly 20.
The needle valve assembly 20 includes a needle valve 50 and a needle valve return spring 52.
A portion of the needle valve 50 is disposed in an annular fuel passage commonly referred to as a kidney 54. The kidney 54 is in fluid communication with the high pressure fuel passage 48. A circumferential opening surface 56 is defined on the needle valve 50 and resides in the kidney 54. A depending circumferential fuel passage 58 fluidly connects the kidney 54 to injection orifice(s) 60 defined in the housing 12. The orifice 60 is in fluid communication with a combustion chamber serviced by the injector 10. The pointed tip 61 of the needle valve 50 acts to selectively open and close the orifice(s) 60.
A translatable spring seat 62 bears on the upper margin of the needle valve 50 and transmits a closing bias exerted by the needle valve return spring 52 on the needle valve. In a preferred embodiment, the spring seat 62 is formed as a component separate and distinct from the needle valve 50.
The spring seat 62 has an upper margin 64 and a lower margin 65, the lower margin 65 bearing on the upper margin of the needle valve 50. A shoulder 66 is disposed between the upper and lower margins 64, 65 and provides a seat for the return spring 52. The spring seat 62 is translatably disposed within a spring cage 68 that is defined in the injector module 14. The spring cage 68 is vented to ambient by vent 70. The fuel being vented from the spring cage 68 by vent 70 flows to ambient in the annular space defined between the housing 12 and the injector module 14.
In operation at initiation of an injection event, the spool 22 is shifted responsive to an actuation command directed to a solenoid 24. The spool 22 is shifted from a closed, venting disposition to an actuation disposition. In the actuation disposition, the spool 22 fluidly connects actuation fluid inlet 26 to the actuation fluid passageway 30. Actuation fluid floods the actuation chamber 38 and generates a significant downward force on the piston head 36. This force overcomes the bias exerted by the intensifier return spring 40 and the piston 32 and plunger 34 commence to stroke downward.
The downward stroke of the plunger 34 acts to compress the volume of fuel residing in the plunger chamber 44 and the high pressure fuel passage 48. The ratio of areas of the piston head 36 to the plunger head 42 determines the amount of compression of the volume of fuel residing in the plunger chamber 44. In practice, the fuel pressure is raised from near ambient (about 50 psi) to an injectable pressure that may be as high as 20,000 psi.
The injectable pressure of the fuel is transmitted via the high pressure fuel passage 48 to the kidney 54. The injectable pressure fuel acts upward on the opening surface 56 and on the surface of the tip 61 in opposition to the bias exerted by the needle valve return spring 52. The force generated on the opening surface 56 and on the tip 61 acts to shift the needle valve 50 upward, withdrawing the tip 61 from the orifices 60 and thereby effecting injection of fuel via the orifices 60 into the combustion chamber.
The end of injection is signaled by a further command to the solenoid 24 that effects a shifting of the spool 22 from the actuation disposition to the vent disposition.
In the vent disposition, the spool 22 fluidly couples the actuating fluid passageway 30 to the vent 28. This results in the actuation fluid in the actuation chamber 38 venting to ambient via the vent 28. With the removal of pressure in the actuation chamber 38, the intensifier return spring 40 acts upward on the piston 32 and plunger 34, returning the piston 32 and plunger 34 to the initial disposition.
Fuel pressure in the plunger chamber 44 drops dramatically with the upward motion of the plunger 34. Fuel pressure acting on the opening surface 56 and on tip 61 decays to the point where the needle valve return spring 52 is able to shift the needle 50 downward and the top 61 closes off the orifices 60, thereby ending the injection event. With the decay of pressure in plunger chamber 44, the checked fuel refill 46 opens and the plunger chamber 44 is refilled with fuel from the fuel gallery in readiness for the next injection event.
Spring closing needle type fuel injectors, such as prior art injector 10, rely on venting of the actuation chamber 38 by the spool 22 (the fuel pressure decay process) and subsequent return actuation of the piston 32 and plunger 34 by the intensifier return spring 40 to end the injection process. The needle valve 50 is then closed solely by the needle valve return spring 52.
It is desirable to minimize the emission of noxious combustion by products to have the most rapid end of injection that is possible. In conventional spring closing needle design as described above. With reference to injector 10, in order to have a faster end of injection, the design is constrained to either use a heavier needle valve return spring 52 or to improve the fuel pressure decay process. The fuel pressure decay process generally is limited by the response of the spool 22 of the control valve assembly 16. A disadvantage of utilizing a heavier needle valve return spring 52 is that the needle valve 50 then is constrained to open only at a much higher injector pressure level (VOP level) necessary to overcome the bias exerted by the increased spring force of the needle valve return spring 52. A higher VOP normally carries with it a significant penalty on engine noise emissions, especially at idle conditions. Such noise is the noise emitted by a combustion ignition engine at idle operating condition and is found to be very objectionable by the consuming public.
There is a need in the industry to improve the end of injection process. Any proposed improvement to the end of injection process should also be cognizant of effecting needle valve opening at the lowest possible fuel pressure in order to improve engine idle noise emissions.